FIG. 12 shows a shoe press apparatus in the press part of a papermaking machine. In this shoe press apparatus, a pair of felts F, and an endless, air-impermeable, elastic belt B, are pinched in a nip N comprising a press roll P and shoe S. When the press roll P rotates in the direction of arrow P′, the elastic belt B also rotates in the direction of arrow B′. A wet paper web W passing through the nip N is pinched between the pair of felts F, and water is squeezed from the web. Oil is supplied to the inside of the elastic belt B to reduce friction against the shoe S.
Since the surface of the shoe S used in this shoe press apparatus conforms to the outer surface of the press roll P, the area of the nip is large compared with that of a press apparatus comprising a pair of press rolls (not shown), and a greater water squeezing effect can be achieved. Therefore, this shoe press apparatus has the advantage that less fuel is required for drying the wet paper web W after water is squeezed from it.
FIG. 13 is an enlarged cross-sectional view showing the structure of an elastic belt B used in the above-mentioned shoe press apparatus. As shown in FIG. 13, the elastic belt B comprises a base member b, and high molecular weight elastic members e, provided on both sides of the base member b. The base member b imparts strength to the elastic belt B as a whole. A woven fabric having a warp and weft is used for the base member. The high molecular weight members e are composed of a resin, such as a urethane resin, having a Shore hardness A of 70 to 98 degrees. Both the felt-contacting surface and the shoe-contacting surface of the elastic belt are composed of such resins. The water squeezed from a wet paper web W in the nip N of a shoe press apparatus may be held in a plurality of grooves provided on the felt-contacting surface of an elastic belt B.
When the elastic belt B having the above-described structure is provided in a shoe press apparatus, compressed air is supplied to the inside of the belt to expand the belt into a cylindrical shape.
At the nip N of the shoe press apparatus, part of the water squeezed from a wet paper web W moves to the elastic belt B through the felts F, which pinch the wet paper web. While most of the water which moves to the elastic belt B is shaken off in the direction of the arrow a of FIG. 12 as a result of the movement of the belt, part of the water sometimes continues to adhere to the belt and re-enters the press part. Thus, water adhering to the elastic belt B may not be removed adequately from the wet paper web W.
It is conceivable that a doctor blade, of the kind used to removes water adhering to the roll, may be used to remove water from the an elastic belt B. Metallic doctor blades, and doctor blades wherein a felt is impregnated with a wear-resistant synthetic material comprising rubber or resin, have been used to remove water from rolls, as disclosed in Unexamined Japanese Patent Publication No. 20697/1981. However such doctor blades to not exhibit good water removal capabilities when used with an elastic belt.
Although a metallic doctor blade can remove water from an elastic belt B, it has a problem in that it causes the elastic belt B to wear out rapidly. Moreover, when an elastic belt B is expanded by compressed air supplied to the inside of the belt, its exterior surface tends to become bowed, and is not necessarily straight in the cross machine direction. Therefore it is difficult to achieve uniform contact between a metallic doctor blade and the elastic belt. There is also a risk of damaging the elastic belt by digging the tip of the metallic doctor blade into the elastic belt.
On the other hand, a doctor blade comprising a felt impregnated with a wear-resistant synthetic resin exhibits excellent adhesion to the surface of an elastic belt, and may be capable of removing water from the surface the belt. However, when this doctor blade is used with an elastic belt having grooves, water may not be removed from the grooves adequately, since the fibers of the doctor blade may not enter the grooves.